In general, an encoder is a device that detects a displacement, a rotation direction, and an angle. The encoder is also used in a vehicle, and the encoder is installed on a bearing device so as to detect the number of revolutions and a rotation direction of a wheel.
In the case of the existing wheel bearing, information on rotation speed is sensed by an ABS sensor from a serrated variation in height by applying a sintered wheel or a Preston wheel, but in the case of a magnetic encoder type wheel bearing, information on rotation speed is sensed by the ABS sensor from a variation in N/S poles of a magnet using a ferrite rubber magnet.
FIG. 1 is a perspective view of a magnetic encoder 10 in the related art, and FIG. 2 is a cross-sectional view of the magnetic encoder in the related art in a radial direction.
The magnetic encoder 10 in the related art includes a ring-shaped back plate 12 which has a cross section in the radial direction that is nearly vertically bent, and ring-shaped magnet rubbers 14 in which N poles and S poles are alternately arranged, and the magnet rubbers 14 are coupled to a rear surface of the back plate 12 along a circumference of the ring.
In general, the magnetic encoder is made of a rubber magnet (or a plastic magnet), and has a width of 5 to 6 mm, a thickness of 0.8 to 1.1 t, and a minimum outer diameter of φ62.
In a case in which it is necessary to improve output performance of the ABS sensor that uses the magnetic encoder, magnetic flux density (intensity of magnetism) of the encoder is increased.
FIGS. 3 to 5 illustrate a method of increasing the magnetic flux density. FIG. 3 is a view illustrating a case in which a material of the encoder is changed to a material (for example, a rare-earth magnet) having high magnetic flux density and large coercive force, FIG. 4 is a view illustrating a case in which an outer diameter of the magnetic encoder is increased, and FIG. 5 is a view illustrating a method of increasing a thickness of the magnetic encoder.
However, the method of increasing the magnetic flux density has problems in that costs are increased in comparison with the existing ferrite magnet when the material is changed (rare-earth magnet), the existing layout is changed when the outer diameter is increased, and costs are increased because an amount of input material is increased when the thickness is increased.